The present invention relates generally to a joint assembly of the type suitable for transmitting torque between a pair of shaft members and the invention is more particularly concerned with a homokinetic joint assembly of the type wherein an inner joint member and an outer joint member have cooperatively interposed therebetween ball members held in a cage which extends concentrically with said inner and outer joint members between an inner surface of the outer joint member and an outer surface of the inner joint member.
Generally, joint assemblies of the type to which the present invention relates include an outer joint member with an inner cavity defined by an interior wall including at least a partially spherical configuration. The interior wall of the outer joint member is formed with grooves which cooperate with complementary grooves formed in the exterior wall of an inner joint member arranged within the cavity of the outer joint member. The grooves of the inner joint member and of the outer joint member correspond in numbers and the arrangement is such that each groove of one of the members cooperates with one groove of the other member to engage therebetween one of the ball members each of which are retained in ball retention apertures of the cage. The cavity of the outer joint member is open on one side thereof and the cooperating grooves of the inner and outer joint members are configured to form a ball member receiving recess which expands in a jaw-like configuration toward the opening direction of the outer joint member cavity. The jaw-like configuration directs the ball members into the angle-bisecting plane. The exterior wall of the cage is generally spherical and is guided in the cavity of the outer joint member while the interior wall of the cage which is also spherical is guided along the spherical outer wall of the inner joint member.
In certain existing prior art joints of the type to which the present invention relates, for example, joints described in German PS No. 1,298,785 or German PS No. 1,267,915, the spherical interior wall of the outer joint member and the spherical exterior wall of the inner joint member present identical overlapping areas with respective cooperating spherical surfaces of the cage. Such arrangements involve the disadvantage that they cannot uniformly insure at all times full lubrication for the co-acting surfaces. If the lubricant film provided in such joint assemblies breaks there may develop a particularly serious risk of damage or of failure of the joint due to the excessive friction which could develop under such circumstances. A further disadvantage of joints of this type resides in the fact that, owing to the varying depth of the grooves which are provided and therefore due to the irregular geometry of the workpiece, the inner joint member can be provided with a duly hardened surface only by means of a very expensive and complicated thermal bath hardening process to produce a tension-fissure and distortion-free workpiece.
Furthermore, in joints of the type involved herein, it has been proposed in the prior art to facilitate the assembly of the joint by extending one of the ball retention apertures of the cage a sufficient distance in the circumferential direction of the cage that the web or spline part of the inner joint member may be inserted through this aperture or recess thereby allowing the inner joint member to be fitted within the cage. This type of approach, in the assembled condition of the joint, leaves only a very small amount of clearance between the exterior surface of the cage and the interior walls of the outer joint member and likewise between the interior surface of the cage and the exterior wall of the inner joint member.
As an alternative to such an extension of one of the cage ball retention apertures, it has also been suggested to make one of the web parts of the inner joint member of an axially shorter length than the remaining webs and than the length of the associated cage ball retention apertures. However, these earlier proposals entail considerable disadvantages because, on the one hand, they result in a significant weakening of the structure of the cage thereby reducing the service life and operational safety of the joint assembly and, on the other hand shortening of one of the web parts may only be obtained by awkward production methods which involve uneconomic cost considerations.
Under such a situation it is the aim of the present invention to provide a non-sliding joint which, as a result of improved lubrication characteristics, is capable of absorbing greater axial forces. Furthermore, it is an aim of the invention to enable the hardening of the inner joint member in a way which is more economically advantageous while at the same time permitting a straightforward assembly of the joint even with a simple cage structure capable of being easily manufactured.